Silicon substrate for solar cell and manufacturing method therefor

ABSTRACT

Disclosed are a silicon substrate for a solar cell and a method of manufacturing the same, wherein the reflectance of solar light can be decreased by gap-filling with AZO, and electrical properties, especially resistivity, can be reduced through e-beam irradiation, thus maximizing the cell efficiency and improving the electrical properties of AZO applied to a silicon solar cell.

TECHNICAL FIELD

The present invention relates to a silicon substrate for a solar celland a method of manufacturing the same and, more particularly, to asilicon substrate for a solar cell and a method of manufacturing thesame, wherein the reflectance of solar light may be decreased bygap-filling with AZO (Al-doped ZnO), and electrical properties,especially resistivity, may be reduced through irradiation with ane-beam, thus maximizing the cell efficiency and improving the electricalproperties of AZO applied to a silicon solar cell.

BACKGROUND ART

With the current increase in greenhouse gas emission reductionobligations through conventions on climate change, carbon dioxidemarkets have become activated, and thus new renewable energy isreceiving attention.

Examples of new renewable energy may include solar light, wind power,biomass, geothermal power, water power, tidal power, etc. In particular,a solar cell is a system for producing electricity using solar light,which is an infinite clean energy source, the rapid growth of which isexpected, and such a solar cell functions to directly convert light intoelectricity.

Also, solar cells are the only power source that decreases powergeneration costs, and adopt the energy that obviates the construction ofpower plants, incurs only maintenance costs, and is safe andenvironmentally friendly, unlike nuclear energy.

A variety of kinds of solar cells are provided, which include typicalcrystalline solar cells, CIGS as thin-film-type solar cells, and DSSC asnext-generation solar cells.

A silicon thin-film solar cell includes an amorphous silicon (a-Si:H)solar cell, which was first developed and distributed, and amicrocrystalline silicon (μc-Si:H) solar cell for increasing lightabsorption efficiency.

A substrate for a solar cell is configured such that a p-typesemiconductor and an n-type semiconductor are provided on respectivesides of a very thin layer comprising a semiconductor monocrystal. Inthis case, a p-n junction is formed at the region where anode andcathode semiconductors are in contact with each other, that is, a regionwhere a p-type semiconductor is in contact with an n-type semiconductor,and positive voltage and negative voltage are respectively applied to ap-type portion and an n-type portion, whereby current flows.Furthermore, specific properties such as rectification of the p-njunction at the interface thereof may be utilized in many semiconductordevices, such as diodes or transistors.

In the use of solar cells to date, indium tin oxide (ITO), configuredsuch that a trace amount of tin (Sn), having superior electricalresistivity and high transmittance, is contained in indium oxide(In₂O₃), has been mainly used in the form of a thin film as atransparent conductive oxide (TOO). However, since the indium materialis very expensive and reserves thereof are limited, a ZnO-based thinfilm, which has low material cost, high transmittance in the IR andvisible light ranges, high electrical conductivity and superior plasmadurability, is being used to replace the ITO transparent conductive thinfilm. However, when the ZnO-based thin film is exposed to air for a longperiod of time, the electrical properties thereof may change due to theeffect of oxygen, and it is not stable in high-temperature atmospheres.Hence, in order to alleviate such defects, there has been recentlyintroduced an Al-doped ZnO (AZO) thin film configured such that ZnO,having high light transmittance in the visible light range,comparatively low electrical resistivity, and high chemical stability tohydrogen plasma, is doped with a small amount of Al.

Typically, the visible light transmittance and electrical resistance ofa transparent electrode material such as AZO vary depending on thefilm-forming conditions, including deposition equipment, substratetemperature, etc. The transparent electrode using AZO is manufacturedthrough chemical vapor deposition, DC and RF sputtering, activatedreactive evaporation (ARE) or the like. Although RF sputtering is knownto be an optimal deposition process for realizing high electricalconductivity, there are no systematic reports for the optimal formationconditions thereof.

In a silicon solar cell in particular, a great amount of light has to beabsorbed into silicon of the solar cell. Although silicon may beadvantageously easily obtained compared to cadmium or telluride, whichis a material for a high-efficiency thin-film solar cell, it has arelatively high refractive index, and thus 20 to 30% of incident lightis undesirably reflected again without producing electric charges. Thereflection of light is known to be decreased through an anti-reflectivelayer or a texturing process, but methods of more efficiently decreasingthe reflection of light from the surface of the solar cell are stillrequired.

DISCLOSURE Technical Problem

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the related art, and an object of thepresent invention is to provide a method of manufacturing a siliconsubstrate for a solar cell, in which a microstructured silicon substrateis subjected to AZO deposition to realize gap-filling, thereby reducingthe reflectance thereof.

Another object of the present invention is to provide a method ofmanufacturing a silicon substrate for a solar cell, in which amicrostructured silicon solar cell is subjected to AZO depositionthrough sputtering and irradiation with an e-beam, thereby improving theelectrical properties thereof.

Technical Solution

The present invention provides a silicon substrate for a solar cell,configured such that a silicon substrate having a microwire structure isdeposited with AZO so as to gap-fill spaces between microwires with theAZO, and is irradiated with an e-beam.

Also, the silicon substrate may be configured such that a p-type siliconsubstrate is doped with an n-type dopant to form a p-n junction.

Also, the p-layer of the silicon substrate may be doped with aluminum toform an aluminum back-surface field (Al-BSF).

Also, the microwires of the silicon substrate may have a height of 0.5to 1.0 μm, a width of 1.5 to 6 μm, and a spacing of 2 to 6 μmtherebetween.

Also, the AZO may be deposited to a thickness of 0.2 to 1.0 μm.

Also, the e-beam may be applied at an intensity of 1 to 4 keV for aperiod of time ranging from 50 to 450 sec.

In addition, the present invention provides a method of manufacturing asilicon substrate for a solar cell, comprising: manufacturing amicrostructured silicon substrate by forming microwires to protrude at apredetermined spacing on a flat base; gap-filling spaces between themicrowires by depositing AZO on the microstructured silicon substrate;and irradiating the silicon substrate having the gap-filled microwireswith an e-beam.

Also, the microwires of the microstructured silicon substrate may beformed using an etching process.

Also, the microstructured silicon substrate may be manufactured byforming a p-n junction of a p-type silicon substrate and an n-typesilicon substrate.

Also, the p-layer of the microstructured silicon substrate may be dopedwith aluminum to form an aluminum back-surface field (Al-BSF).

Also, the microwires of the microstructured silicon substrate may have aheight of 0.5 to 1.0 μm, a width of 1.5 to 6 μm, and a spacing of 2 to 6μm therebetween.

Also, in the gap-filling the spaces between the microwires, the AZO maybe deposited on the microstructured silicon substrate using any oneprocess selected from among DC sputtering, RF sputtering, chemical vapordeposition, pulsed laser deposition, and activated reactive evaporation(ARE).

Also, in the gap-filling the spaces between the microwires, the AZO maybe deposited to a thickness of 0.2 to 1.0 μm.

Also, the e-beam may be applied at an intensity of 1 to 4 keV for aperiod of time ranging from 50 to 450 sec.

Advantageous Effects

According to the present invention, the silicon substrate for a solarcell is configured such that the spaces between microwires of thesilicon substrate are gap-filled with AZO, thereby decreasing thereflectance of solar light.

Also, the silicon substrate, the microstructure of which is gap-filledwith AZO, is irradiated with an e-beam, thereby altering the electricalproperties thereof, in particular lowering the resistivity thereof.

Additionally, a solar cell having significantly improved electricalproperties and a low price can be effectively manufactured using thesilicon substrate having lowered reflectance and resistivity.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a silicon substrate for asolar cell according to an embodiment of the present invention;

FIG. 2 is a flowchart illustrating the process of manufacturing asilicon substrate for a solar cell according to the present invention;

FIGS. 3 to 5 are scanning electron microscope (SEM) images illustratingsilicon substrates having a microwire structure with a height of 0.7 μm,a width of 2 to 6 μm, and a spacing of 6 μm between microwires, afterAZO deposition and e-beam irradiation at 2 KeV;

FIGS. 6 to 8 are SEM images illustrating silicon substrates having amicrowire structure with a height of 0.7 μm, a width of 2 to 6 μm, and aspacing of 6 μm between microwires, after AZO deposition and e-beamirradiation at 3 KeV;

FIGS. 9 to 11 are graphs illustrating the results of measurement of aHall effect depending on the irradiation time of an e-beam at 2 KeV insilicon substrates having a microwire structure with a height of 0.7 μm,a width of 2 to 6 μm, and a spacing of 6 μm between microwires;

FIGS. 12 to 14 are graphs illustrating the results of measurement of aHall effect depending on the irradiation time of an e-beam at 3 KeV insilicon substrates having a microwire structure with a height of 0.7 μm,a width of 2 μm, and a spacing of 6 μm between microwires;

FIGS. 15 to 17 are graphs illustrating the reflectance of siliconsubstrates having a microwire structure with a height of 0.7 μm, a widthof 2 to 6 μm, and a spacing of 6 μm between microwires, after e-beamirradiation at 2 KeV; and

FIGS. 18 to 20 are graphs illustrating the reflectance of siliconsubstrates having a microwire structure with a height of 0.7 μm, a widthof 2 to 6 μm, and a spacing of 6 μm between microwires, after e-beamirradiation at 3 KeV.

MODE FOR INVENTION

Hereinafter, a detailed description will be given of preferredembodiments of the present invention through the appended drawings.Throughout the drawings, the same reference numerals refer to the sameor like elements or parts. In the following description of the presentinvention, detailed descriptions of known constructions and functionsincorporated herein will be omitted when they may make the gist of thepresent invention unclear.

It will be understood that when a particular allowable error inmanufacturing and materials is presented in meaning, the terms “about”and “substantially” are used to mean a numerical value or a proximatevalue to the numerical value. The terms are also used to help theunderstanding of the present invention and to prevent the unfair use ofthe disclosure mentioning an accurate or absolute numeral value.

FIG. 1 is a cross-sectional view illustrating a silicon substrate for asolar cell according to an embodiment of the present invention, FIG. 2is a flowchart illustrating the process of manufacturing a siliconsubstrate for a solar cell according to the present invention, FIGS. 3to 5 are SEM images illustrating silicon substrates having a microwirestructure with a height of 0.7 μm, a width of 2 to 6 μm, and a spacingof 6 μm between microwires, after AZO deposition and e-beam irradiationat 2 KeV, FIGS. 6 to 8 are SEM images illustrating silicon substrateshaving a microwire structure with a height of 0.7 μm, a width of 2 to 6μm, and a spacing of 6 μm between microwires, after AZO deposition ande-beam irradiation at 3 KeV, FIGS. 9 to 11 are graphs illustrating theresults of measurement of a Hall effect depending on the irradiationtime of an e-beam at 2 KeV in silicon substrates having a microwirestructure with a height of 0.7 μm, a width of 2 to 6 μm, and a spacingof 6 μm between microwires, FIGS. 12 to 14 are graphs illustrating theresults of measurement of a Hall effect depending on the irradiationtime of an e-beam at 3 KeV in silicon substrates having a microwirestructure with a height of 0.7 μm, a width of 2 μm, and a spacing of 6μm between microwires, FIGS. 15 to 17 are graphs illustrating thereflectance of silicon substrates having a microwire structure with aheight of 0.7 μm, a width of 2 to 6 μm, and a spacing of 6 μm betweenmicrowires, after e-beam irradiation at 2 KeV, and FIGS. 18 to 20 aregraphs illustrating the reflectance of silicon substrates having amicrowire structure with a height of 0.7 μm, a width of 2 to 6 μm, and aspacing of 6 μm between microwires, after e-beam irradiation at 3 KeV.

n the silicon substrate having a microwire structure for a solar cellaccording to the present invention, the silicon substrate having amicrowire structure is deposited with AZO so as to gap-fill the spacesbetween the microwires with AZO, and is irradiated with an e-beam.

As illustrated in FIG. 1, the silicon substrate 100 is configured suchthat a p-type silicon substrate 120 is doped with an n-type dopant 130to form a p-n junction, and the silicon substrate 100 has microwiresthat are formed to protrude therefrom to thus enlarge the area where thep-n junction is formed, and the area may be further enlarged with anincrease in the density and aspect ratio of the wires.

Furthermore, aluminum is doped on the back surface of the p-type siliconsubstrate 120, which is not doped with the n-type dopant 130 of thesilicon substrate 100, thus forming an aluminum back-surface field(Al-BSF) 110. The formation of the Al-BSF 110 is a process for improvingthe efficiency of a silicon solar cell, and the back surface of thep-type silicon substrate of the silicon substrate for use in a solarcell is doped at a high concentration, thus generating a difference inpotential and impeding the transfer of a small number of carriers to theback surface, thereby decreasing the rate of recombination on the backsurface. Accordingly, the open voltage is increased and the fill factormay be increased.

The height (h of FIG. 1) of the microwires of the silicon substrate 100,the width (w of FIG. 1) thereof, and the spacing (s of FIG. 1) betweenthe microwires are not particularly limited, so long as they fall withinthe micro-unit range. Preferably, the microwires have a height h of 0.5to 1.0 μm, a width of 1.5 to 6 μm, and a spacing of 2 to 6 μmtherebetween.

The AZO 200, which is deposed on the silicon substrate 100 to realizegap-filling, is a transparent conductive oxide (TCO). As for a siliconsubstrate for a solar cell in which AZO is deposited on a siliconsubstrate having no microwires, the produced electrons may be lost atthe interface between the silicon substrate and the AZO. However, whenthe AZO 200 is deposited on the silicon substrate 100 having microwiresaccording to the present invention, collection of the carriers producedby light may be increased. Furthermore, recombination of the carriersmay be minimized compared to the silicon substrate having no microwires.

The AZO 200 is preferably deposited to a thickness of 0.2 to 1.0 μm.

The resistivity may be decreased by radiating an e-beam onto the siliconsubstrate having the AZO 200 deposited thereon. This is because thecrystal size of the AZO 200 of the silicon substrate is increasedthrough e-beam irradiation.

As illustrated in FIG. 2, the silicon substrate for a solar cellaccording to the present invention may be manufactured by forming amicrostructured silicon substrate, configured such that microwires areformed to protrude at a predetermined spacing on a flat base, depositingAZO on the microstructured silicon substrate so that the spaces betweenthe microwires are gap-filled therewith, and radiating an e-beam ontothe silicon substrate in which the spaces between the microwires aregap-filled.

As illustrated in FIG. 3, the microstructured silicon substrate 100 maybe manufactured by forming microwires using an etching process. Theetching process may include any one selected from the group consistingof electrochemical etching, solution etching, and metal catalyticetching.

The microstructured silicon substrate 100 may be manufactured in amanner in which the p-n junction is formed and the Al-BSF 110 is formedon the back surface of the p-type silicon substrate 120, which is notdoped with the n-type dopant 130. The height h, width w and spacing s ofthe microwires of the silicon substrate 100 are not particularly limitedwithin the micro-unit range, but the microwires preferably have a heighth of 0.5 to 1.0 μm, a width of 1.5 to 6 μm, and a spacing of 2 to 6 μmtherebetween.

In the gap-filling step, AZO is deposited on the microstructured siliconsubstrate 100 using any one process selected from among DC sputtering,RF sputtering, chemical vapor deposition, pulsed laser deposition, andactivated reactive evaporation (ARE). Particularly useful is DCsputtering or RF sputtering.

The AZO, which is deposited on the silicon substrate 100 to realizegap-filling, is preferably formed to a thickness of 0.2 to 1.0 μm, asmentioned above.

In the e-beam irradiation step, an e-beam is applied to increase thecrystal size of the AZO 200 of the silicon substrate so as to decreaseresistivity, as mentioned above, and the e-beam may be applied at anintensity of 1 to 4 keV, and preferably 2 keV, for a period of timeranging from 50 to 450 sec.

A better understanding of the present invention may be obtained throughthe following examples regarding the silicon substrate for a solar cell,which are set forth to illustrate, but are not to be construed to limitthe present invention.

Manufacture of Silicon Substrate Having Microwire Structure for SolarCell

Silicon substrates were manufactured in a manner in which microwireswere formed through etching of a p-type silicon substrate so as to havea height h of about 0.7 μm, a spacing s of 6 μm therebetween and a widthw of 2, 4, and 6 μm, and an n-type dopant was then doped thereon to forma p-n junction, after which the back surface of the p-type siliconsubstrate, which had not been doped with the n-type dopant of thesilicon substrate, was doped with Al.

Deposited on the silicon substrate having microwires was AZO usingsputtering.

Example 1

The silicon substrates having microwires at a width w of 2, 4 and 6 μm,manufactured in the manufacture of the silicon substrate having amicrowire structure as described above, were irradiated with an e-beamat a DC power of 2 keV for 60, 180, 300, and 420 sec.

In FIGS. 3 to 5, (a) shows the substrates before deposition of AZO inthe manufacture of the silicon substrate having a microwire structure asabove, (b) shows the substrates after the deposition of AZO but beforee-beam irradiation, (c) shows the substrates after e-beam irradiationfor 60 sec, (d) shows the substrates after e-beam irradiation for 180sec, (e) shows the substrates after e-beam irradiation for 300 sec, and(f) shows the substrates after e-beam irradiation for 420 sec.

FIG. 3 illustrates SEM images of the silicon substrates havingmicrowires with a height of 0.7 μm, a width of 2 μm, and a spacing of 6μm therebetween, after deposition of AZO and e-beam irradiation at 2KeV.

FIG. 4 illustrates SEM images of the silicon substrates havingmicrowires with a height of 0.7 μm, a width of 4 μm, and a spacing of 6μm therebetween, after deposition of AZO and e-beam irradiation at 2KeV.

FIG. 5 illustrates SEM images of the silicon substrates havingmicrowires with a height of 0.7 μm, a width of 6 μm, and a spacing of 6μm therebetween, after deposition of AZO and e-beam irradiation at 2KeV.

As illustrated in FIGS. 3 to 5, (a) shows the substrates before thedeposition of AZO in the manufacture of the silicon substrate having amicrowire structure as above, (b) shows the substrates after thedeposition of AZO but before e-beam irradiation, (c) shows thesubstrates after e-beam irradiation for 60 sec, (d) shows the substratesafter e-beam irradiation for 180 sec, (e) shows the substrates aftere-beam irradiation for 300 sec, and (f) shows the substrates aftere-beam irradiation for 420 sec.

Example 2

The silicon substrates having microwires at a width w of 2, 4 and 6 μm,manufactured in the manufacture of the silicon substrate having amicrowire structure as described above, were irradiated with an e-beamat a DC power of 3 keV for 60, 180, 300, or 420 sec.

In FIGS. 6 to 8, (a) shows the substrates before the deposition of AZOin the manufacture of the silicon substrate having a microwire structureas above, (b) shows the substrates after the deposition of AZO butbefore e-beam irradiation, (c) shows the substrates after e-beamirradiation for 60 sec, (d) shows the substrates after e-beamirradiation for 180 sec, (e) shows the substrates after e-beamirradiation for 300 sec, and (f) shows the substrates after e-beamirradiation for 420 sec.

FIG. 6 illustrates SEM images of the silicon substrates havingmicrowires with a height of 0.7 μm, a width of 2 μm, and a spacing of 6μm therebetween, after the deposition of AZO and e-beam irradiation at 3KeV.

FIG. 7 illustrates SEM images of the silicon substrates havingmicrowires with a height of 0.7 μm, a width of 4 μm, and a spacing of 6μm therebetween, after the deposition of AZO and e-beam irradiation at 3KeV.

FIG. 8 illustrates SEM images of the silicon substrates havingmicrowires with a height of 0.7 μm, a width of 6 μm, and a spacing of 6μm therebetween, after the deposition of AZO and e-beam irradiation at 3KeV.

Evaluation of Properties of Silicon Substrate

(1) Evaluation Method

The Hall effect is the production of an electromotive force in adirection orthogonal to current and a magnetic field when the magneticfield is applied perpendicular to the current, and represents thecarrier density, mobility, and resistivity depending on the e-beamirradiation time.

(2) Results

FIGS. 9 to 11 are graphs illustrating the results of measurement of theHall effect depending on the irradiation time of an e-beam at 2 keV inthe silicon substrates having microwires with a height of 0.7 μm, awidth of 2 to 6 μm and a spacing of 6 μm therebetween, in which FIGS. 9,10 and 11 are graphs illustrating the results of measurement of the Halleffect when the width is 2 μm, 4 μm, and 6 μm, respectively.

FIGS. 12 to 14 are graphs illustrating the results of measurement of theHall effect depending on the irradiation time of an e-beam at 3 keV inthe silicon substrates having microwires with a height of 0.7 μm, awidth of 2 to 6 μm and a spacing of 6 μm therebetween, in which FIGS.12, 13 and 14 are graphs illustrating the results of measurement of theHall effect when the width is 2 μm, 4 μm, and 6 μm, respectively.

As is apparent from the graphs, when the e-beam irradiation time wasincreased, resistivity was decreased, and was not further lowered due tosaturation after the lapse of a predetermined period of time.

2. Spectrophotometry

(1) Evaluation Method

The maximum light absorption wavelength of the molecule is measuredusing a spectrophotometer, the reflectance is represented in units of %,and the average is obtained by averaging the reflective values of 300 to1800 nm corresponding to the total wavelength range.

(2) Results

FIGS. 15 to 17 are graphs illustrating the reflectance of the siliconsubstrates having microwires with a height of 0.7 μm, a width of 2 to 6μm and a spacing of 6 μm therebetween, after e-beam irradiation at 2keV. Here, FIGS. 15, 16 and 17 are graphs illustrating the reflectancewhen the width is 2 μm, 4 μm, and 6 μm, respectively.

FIGS. 18 to 20 are graphs illustrating the reflectance of the siliconsubstrates having microwires with a height of 0.7 μm, a width of 2 to 6μm and a spacing of 6 μm therebetween, after e-beam irradiation at 3keV. Here, FIGS. 18, 19 and 20 are graphs illustrating the reflectancewhen the width is 2 μm, 4 μm, and 6 μm, respectively.

As is apparent from FIGS. 15 to 20, the substrate irradiated with ane-beam according to the present invention can exhibit very lowreflectance of solar light compared to a substrate having no AZOdeposited thereon.

1. A silicon substrate for a solar cell, configured such that a siliconsubstrate having a microwire structure is deposited with AZO (Al-dopedZnO) so as to gap-fill spaces between microwires with the AZO, and isirradiated with an e-beam.
 2. The silicon substrate of claim 1, whereinthe silicon substrate is configured such that a p-type silicon substrateis doped with an n-type dopant to form a p-n junction.
 3. The siliconsubstrate of claim 1, wherein a p-layer of the silicon substrate isdoped with aluminum to form an aluminum back-surface field (Al-BSF). 4.The silicon substrate of claim 1, wherein the microwires of the siliconsubstrate have a height of 0.5 to 1.0 μm, a width of 1.5 to 6 μm, and aspacing of 2 to 6 μm therebetween.
 5. The silicon substrate of claim 1,wherein the AZO is deposited to a thickness of 0.2 to 1.0 μm.
 6. Amethod of manufacturing a silicon substrate for a solar cell,comprising: manufacturing a microstructured silicon substrate by formingmicrowires to protrude at a predetermined spacing on a flat base;gap-filling spaces between the microwires by depositing AZO on themicrostructured silicon substrate; and irradiating the silicon substratehaving the gap-filled microwires with an e-beam.
 7. The method of claim6, wherein the microwires of the microstructured silicon substrate areformed using an etching process.
 8. The method of claim 6, wherein themicrostructured silicon substrate is manufactured by forming a p-njunction of a p-type silicon substrate and an n-type silicon substrate.9. The method of claim 6, wherein a p-layer of the microstructuredsilicon substrate is doped with aluminum to form an aluminumback-surface field (Al-BSF).
 10. The method of claim 6, wherein themicrowires of the microstructured silicon substrate have a height of 0.5to 1.0 μm, a width of 1.5 to 6 μm, and a spacing of 2 to 6 μmtherebetween.
 11. The method of claim 6, wherein in the gap-filling thespaces between the microwires, the AZO is deposited on themicrostructured silicon substrate using any one process selected fromamong DC sputtering, RF sputtering, chemical vapor deposition, pulsedlaser deposition, and activated reactive evaporation (ARE).
 12. Themethod of claim 6, wherein in the gap-filling the spaces between themicrowires, the AZO is deposited to a thickness of 0.2 to 1.0 μm. 13.The method of claim 6, wherein the e-beam is applied at an intensity of1 to 4 keV for a period of time ranging from 50 to 450 sec.